Scientists at the University of Southern California (USC) have developed technology to cheaply produce stable liquid solar cells that can be painted or printed onto clear surfaces. The technology relies on solar nanocrystals that are around four nanometers in size - meaning you could fit more than 250 billion on the head of a pin. Their size allows them to be suspended in a liquid solution so they could be printed like a newspaper. The downside, commercialization of this technology is still years away.